Metabolic enzyme inhibitory abilities, in vivo hypoglycemic ability of palmleaf raspberry fruits extracts and identification of hypoglycemic compounds

The unripe palmleaf raspberry, namely Fupenzi (FPZ), is an important medicinal and edible food. This study aims to evaluate the potential of FPZ extracts prepared with different approaches in attenuating hyperglycemia, gout, Alzheimer's disease, and pigmentation, to obtain the enriching fraction and to identify the major active compounds. Results indicated that FPZ extracts showed weak activity against acetylcholinesterase, considerable ability against tyrosinase and xanthine oxidase, but excellent inhibition on α-glucosidase. Ultrasound-assisted 40 % ethanol extract (40EUS) gave the highest phenolics content, and the best α-glucosidase inhibition (IC50 = 0.08 μg/mL), which is 877-fold higher than that of positive control acarbose. The 40 % ethanol eluting fraction of 40EUS showed the strongest a-glucosidase inhibition with the IC50 value of 37.79 ng/mL, it could also effectively attenuate the fasting blood glucose level and oral glucose tolerance of C57BL/6 mice. Twenty-six compounds were identified from 40 % ethanol fraction by using HPLC-QTOF-MS/MS, hydrolysable tannins (including 11 ellagitannins and 4 gallotannins) were the major compounds, phenolic acids came to the second. Above results could provide important technical supporting for the further application and research of FPZ in health foods and drugs against diabetes.